The identification of vehicles at night is required particularly for an automatic light control in a vehicle. It is the aim of an automatic light control to control the intensity and/or direction of one's own vehicle headlights in such a manner that other road users are not dazzled.
An important feature for the identification of vehicles by means of a camera in the dark is the vehicle lighting of oncoming vehicles that is represented in the camera image by spots that have a high intensity.
WO 2008/064621 A1, which is incorporated by reference, shows a method for the identification of reflectors and vehicle lights by means of a camera sensor system in the surroundings of a vehicle. For this purpose, a sequence of images of the surroundings of the vehicle is recorded. At least one light spot in the sequence of images is tracked. The intensity of the light spot in the sequence of images is determined and analyzed. Light spots above a first threshold value are identified as vehicle lights, and light spots below a second threshold value are identified as reflectors.
It has turned out that with some specimens of a commercially available image sensor, this method with preset threshold values is lacking the desired reliability of the identification of vehicle lights/reflectors.
One reason for this is that each specimen of an image sensor has a slightly different sensitivity. On the other hand, the sensitivity of each image sensor is changing in time. These changes may be deteriorations in sensitivity caused by the degradation of, in particular, the colour filters (Bayer pattern) as well as increases in sensitivity, caused particularly by late curing of plastics in the visual range of the image sensor, which makes the field of view clearer.